ipvs: ensure inner headers in ICMP errors are in headroom

In the Linux kernel, the following vulnerability has been resolved: ipvs: ensure inner headers in ICMP errors are in headroom Sashiko points out that after stripping the outer headers with pskb_pull() we should ensure the inner IP headers in ICMP errors from tunnels are present in the skb headroom for functions like ipv4_update_pmtu(), icmp_send() and IP_VS_DBG(). Also, add more checks for the length of the inner headers.